British citizens make up about 25 percent of foreign fighters of the al-Shabab group in Somalia, according to a report by the London-based Royal United Services Institute (RUSI).

“Britons are thought to make up about 25 per cent of the 200 or so foreign fighters that the Al-Shabaab group in Somalia currently fields, and who are engaging in a deepening war on neighboring Kenya and its tourist trade. Most of these individuals appear to be only informally networked, making the most of personal links through Kenya or South Africa,” says the report.

Earlier on February, the UK Prime Minister David Cameron had warned that Britain faced a security threat from radical Somali-born youngsters, with British intelligence agency MI5 confirming that there are currently a "significant number" of Britons training with al-Shabab.

Last January, a Kenyan court issued a warrant of arrest for a British woman, Natalie Faye Webb, for alleged links with al-Shabab fighters.

Furthermore, another British citizen, Jermaine Grant is on trial in Kenya in connection with a bomb plot by the group.

The weak Western-backed transitional government in Mogadishu has been battling al-Shabab fighters for the past five years and is propped up by thousands of African Union forces from Uganda, Burundi, and Djibouti.

Somalia has not had a functioning government since 1991, when warlords overthrew former dictator Mohamed Siad Barre.